The purpose of lubricating the contact surfaces of an anti-ballooning ring is to reduce the friction of the body of a yarn restrained by that ring, thereby making the yarn tension more uniform and, in the case of yarns composed of thermoplastic fibers, also preventing overheating thereof. The term "body of the yarn" is meant to refer to the core of twisted fibers from which individual fiber ends stand out laterally. When only these protruding fiber ends come into contact with the lubricant emerging from one or more outlets on the ring, satisfactory metering of the lubricant can be achieved without any additional measures to insure adequate lubrication of the contact surfaces. The lubricant is preferably a synthetic or, possibly, a natural oil but may also be some other fluid substance.
The anti-ballooning ring serves to restrict the radial excursion of a yarn which is entrained by a rotating spindle coaxial with that ring and passes through a traveler revolving on a spinning or twisting ring encircling the spindle.
Lubricated anti-ballooning rings are known from U.S. Pat. No. 3,638,415 and German laid-open specification No. 2,409,146, for example. In these known devices, the lubricant channels terminate at the contact surfaces against which the rotating yarns are pressed by the centrifugal forces acting on them. If, as in the apparatus according to FIG. 5 of the U.S. patent referred to, the lubricant outlet is formed by an end of a cylindrical bore of very small diameter, arranged halfway up on the contact surface, the upper half of that surface is not lubricated since the downward-traveling yarn conveys the lubricant only to the lower half thereof. Moreover, during any shutdown of the machine, lubricant may flow out from the supply channels onto the contact surfaces and, when the machine is started up again, this may cause excessive lubrication of the yarns, which is undesirable. At other times there is also a danger of excessive lubrication, since the flow of lubricant through the bore cannot be accurately controlled. If an attempt is made to avoid such excessive lubrication by the expedient of making the diameter of the bore extremely small, there is a danger that this bore will become obstructed during operation and then no lubricant at all will come out. In any case, such fine bores are expensive to produce.
As described with reference to FIG. 4 of that U.S. patent, the anti-ballooning ring can be made of sintered metal with lubricant constantly supplied to it from outside. To ensure that sufficient lubricant reaches the contact surface, however, the sintered metal must be relatively large-pored; this means that the areas located outside the contact surface have to be sealed. Lubrication is also uneven and depends to a great extent on the viscosity of the lubricant.